1. Field of the Invention
The present invention relates to a plasma processing apparatus capable of having its status detected and a method for detecting the status of a plasma processing apparatus, and more specifically, relates to a plasma processing apparatus and a method for detecting the status of a plasma processing apparatus capable of having the status of the apparatus such as defect or individual variability of the apparatus detected without performing plasma discharge.
2. Description of the Related Art
Recently, plasma processing apparatuses using plasma for processing are used widely in the processes for manufacturing semiconductor devices and flat panel displays. In plasma processing apparatuses, reactive gases or depositing gases selected according to the object of the process are discharged via microwaves or high frequency waves, for example, so as to process samples. In such apparatuses, the electrons, ions and activated radicals having relatively high energy generated by discharge cause the components in the interior of the processing chamber to be consumed or cause reaction products to be deposited on the inner walls of the processing chamber, which leads to variation of the processing properties. Especially, in manufacturing high-accuracy devices, the variation of processing properties causes serious problems that may lead to deterioration of yield of the products or creation of defective products.
Thus, measures have been taken generally to control the processing status of the plasma processing apparatus highly accurately, or to monitor the status of the generated plasma directly in order to stabilize processing properties. According to conventional techniques for stabilizing the status of plasma, the defect of the apparatus is determined based on the amplitude and phase of reflection coefficient of the high frequency waves for generating plasma reflected from the plasma (refer for example to Japanese Patent Application Laid-Open Publication No. 2002-294460, hereinafter referred to as patent document 1).
Furthermore, a network analyzer is used to measure the s-parameter of a plasma-generating high frequency power supply and matching unit, and based on the information on the measured s-parameter, the matching of the high frequency waves is adjusted so as to control the plasma processing status (refer for example to Japanese Patent Application Laid-Open Publication No. 2005-158684, hereinafter referred to as patent document 2).
Further, a method for monitoring the change in plasma density using a plasma absorption method which is one method for measuring plasma density is proposed to directly monitor the plasma status during processing. The plasma absorption method includes supplying high frequency power to the plasma while changing frequency, and computing the plasma density from the frequency in which the reflected power becomes minimum. This method utilizes the fact that the frequency in which plasma waves are excited depends on the plasma density, and plasma waves are resonantly-excited in the plasma when the reflected power becomes minimum (refer for example to Japanese Patent Application Laid-Open Publication No. 2000-340550, hereinafter referred to as patent document 3).
Similar to the prior art disclosed in patent document 3, a method is proposed to measure the plasma density using an absorption probe method, wherein a network analyzer is used to detect the frequency in which the imaginary part of the reflecting coefficient from the plasma zero-crosses, by which the plasma density can be computed with high accuracy (refer for example to Japanese Patent Application Laid-Open Publication No. 2005-228727, hereinafter referred to as patent document 4).
However, according to prior art plasma processing apparatuses, the control of the apparatus or the determination of defect of the apparatus is always performed based on the data detecting the status of the apparatus during plasma discharge, and since the detected data is influenced by the large number of parameters of the apparatus related to the discharge status, such as gas pressure, processing gas flow rate, processing chamber temperature and deposits on the inner walls of the processing chamber, it is difficult to determine the status of the apparatus accurately.
If the amplitude data and phase data of the reflection coefficient of the high frequency wave used for generating plasma are used to control the apparatus, the obtained information related to the status of the apparatus is only effective for limited portions of the apparatus, since these data mainly reflect the matching status of the high frequency waves from the high frequency power supply.
When the prior art plasma absorption probe method is used to measure the plasma status such as plasma density and to perform control of the apparatus, it is necessary to arrange a sensor for measurement within the plasma-generating region of the chamber, but if the sensor is damaged by the reactive processing gas or if reaction products are deposited on the sensor, particles may contaminate the object being processed.
Moreover, according to the method for controlling the status of the apparatus while measuring data during plasma-generated processing, the manufacturing line must be stopped when the defect of the apparatus is detected, and the manufacturing is stopped during the period of time when the defect of the apparatus is coped with, which may lead to a great loss.